Mass spectrometry



March 6, 1945. C. E, BERRY MASS SPECTROMETRY Filed Aug. 19. 1943@frau/va ATTORNEYJ Patented Mar. 6, 1945 m8 SPEUI'IOMITIY Cliffordtlderry, Pasadena,

denaCallf.,acorperatlenofCalUe|-nh Calihalilnorto Pala ApplicationAllnet 19, 1m, Serial No. 498,287

(u 'II-lll ICIIIBI.

This invention is concerned with mass spettrometers and providesimproved mass markers for such instruments.

A mass spectrometer is an apparatus i'or sorting ions according to theratio of the mass of the ion to the charge that it carries (this ratiobeing referred to hereinafter as speciilc mass) and can be employed forvarious purposes, including qualitative and quantitative analyses ofmixtures containing ditlerent kinds of molecules, determination ofisotope ratios, etc.

A common form of mass spectrometer includes an ionization chamber inwhich molecules oi' the mixture to be analyzed are converted into ions,

an analyzer tube in which a heterogeneoi beam of the ions is separatedby an electric or magnetic field into a plurality of diverginghomogeneous beams of ions (the ions o the same specic mass beingincluded in a single beam), an ion collector, means (referred'to here asa beam sweeper) for bringing the several beams successively into contactwith the collector and means for indicating separately the currentscollected from the several beams.

A record of the separately collected currents is a mass spectrogram,which may take any one of several forms. For example, it may be a graphon which the magnitudes of the currents corresponding to the severalcollected ion beams are represented by the heights of a series of peaksprojecting from an abscissa axis. Such a record can be produced on alaterally moving sheet of photographic paper, or the like, by arecording galvanometer. For some purposes, such a mass spectrogram isentirely adequate, but in many cases, for example in the quantitativeanalysis of a mixture of hydrocarbons containing a number of differentkinds of molecules some of which crack in the ionization chamber to fonna plurality of dlierent kinds of ions, it is necessary to determine andidentify the specific mass of the ions to which each peak corresponds.

In accordance with the invention described and claimed in the copendingapplication orf Robert V. Langmuir Serial No. 494,807, nled July 15.1943, the interpretation oi' a mass spectrogram is facilitated byindicating in a coordinated nunner and preferably simultaneously withthe indication of the peaks (ion currents), the specic masses of theions to which the respective peaks (currents) correspond. Thus Langmuircontemplated marking on the mass spectrogram adjacent the respectivepeaks and during the recording thereof. the specific masses of the ionsto which the peaks correspond.

Inoneformcfthe Lnngmuirapparatuatbe spcciiic mass indicator isoperatively connected wlththebeamsweeperandisactuatedbuit. In auchapparatus. the beam sweeper automatically and gradually alters thepotential impressed upontheionapassing through the analyser andthuachangesthepathoi'theionlsothatthe beams are swept successively overthe collector. Aspeciiicmassindicatorisconnectedinacircuitwlththebeamsweeperandachangein the potential actuatea theindicator. For example, the mass indicator may be a galvanometercalibrated in terms of ion masse or a vacuum tube circuit which istripped at intervals at successive values o( ion accelerating potential.means being provided to mark the spectrogram each time the circuittrips. In this way. the beam sweeper and the mass indicator aresynchronised andthepeaksonthespectrogramarecorrelated withthespeciiic oftheionstowhich they correspond.

Apparatus described in the aforementioned- Iangmuir application includesa beam sweeper which automatically decreases the ion acceleratingpotentials applied to electrodes in the mass spectrometer, and isconnected to these electrodes through a potential divider. This in tumis connected in series with a rotary stepping relay, the contact arm ofwhich is connected to the slider of a potentiometer in a direct currentamplifier circuit. The output of this D. C. ampiiiler is employed tomark the mass spectrogram at points corresponding to the peaks thereon.

As the result of my investigations. I have developed a mass marker whichcorrelates a spci cinc mass and the current oi' the beam to which themass corresponds with great accuracy. In general, my inventioncontemplates in a mass indicator of a mass spectrometer having aresistance, means for impressing across the resistance a voltage whichis a function or the specinc mass being detected, and means forselecting successive fractions of this voltage during a period in whichthe voltage is changing, the combination which comprises means connectedto the voltage selector for producing an alternating currentcorresponding in amplitude to the selected fraction of the voltage. andmeans responsive to a deviation in the amplitude of the alternatingcurrent from a threshold value for indicating the specific mass of ionsdetected when the threshold is reached and lfor causing the voltageselector to select the next fraction of voltage. In its preferred form.my invention contemplates. in combination with the voltage selector, abalanced network. means for couvert-` lng the output of the balancednetwork yinto alternating current. a high gain A. C. ampliner. and meansior rectifying the ampliner output and applying this rectiiled output toa trip circuit which marks the spectrogram.

These and other features o! my invention will be more thoroughlyunderstood in the light of the following detailed description, taken inconjunction with the accompanying drawing, which is a wiring diagram ofa preferred form of my ma marker.

Referring now to the drawing. it will be observed that a massspectrometer l is provided with an ionisation chamber l. an analysertube l. an ion collector I, and an inlet conduit l for the material tobe analysed in the spectrometer. A high voltage from a direct currentsource is applied to the mass spectrometer through a beam sweeper i.Thus the beam sweeper impresses a high but gradually decaying potentialbetween electrodes in the mass spectrometer. Gas moleeules that areionized in the ionisation chamber by bombardment with an electron beam 1are propelled to a slit Si in an accelerating electrode l by a potentialimpressed between pusher electrodes P1, P: and the electrode l. Aheterogene ous ion beam is thus formed and this is further acceleratedinto the analyser tube by a potential impressed between the acceleratingelectrode t and a second accelerating electrode l. which has a slit Sathat matches the slit B1 in the rst accelerating electrode. Thepotential applied. respectively, to the pusher electrodes Pi. Pa may beadjusted -by means oi' a potential divider I I which comprises twopotentiometers in parallel and connected. respectively. to the twopusher electrodes. Ihe potenliometers in parallel are followed by alarge resistance IIA in series. 'I'he sise oi' this resistance. which isconnected to ground through a tapped resistor i 1A of a rotary steppingrelay l2, controls the proportion of the potential applied across thegap P1. Pa-Si and the gap Si-S1. An ammeter I3 is connected in serieswith the resistor IIA oi' the rotary stepping relay and the potentialdivider and may be calibrated in terms of speclilc mass.

The maior portions oi the apparatus, in addition to those alreadydescribed. comprise a balanced network. a high gain A. C. amplier, anoscillator coupled to a vibrator, a trip circuit. and appropriate powersupplies.

The rotary stepping relay conveniently is the type designated byGuardian Electric Manufacturing Company as "Series R steoplne relay. Itcomprises a rotary contact arm Il which upon rotation may touch any oneoi a series of equally spaced circumferentially positioned ilxed tapsT1. Ts. Ts Tas on the resistor. A tap indicating disc or a cylinder 8lrigidly secured to the same shaft as the arm has numbers thereon whichare moved beneath the pointer and become illuminated by a lamp 81 whenthe arm contacts the corresponding tap. Thus, as shown. the numeral I isilluminated on the tap indicator 38 when the rotary arm touches tap Ts.The indicatorllmayalsocarryspecicmassnumbers in addition to tap numbers.

'Iherotarysteppingrclayalsoincludesasteppingil llandaresetcoilll.Whenanelectrical impulse is applied to the stepping coil. the rotarycontact arm moves to the next tap in sequence.Whencurrentisappliedtothereset wiLtberotaryarmreturnstothenrsttappositlmTx.

The contact arm ofthe rotary stepping 'relayisconnectedtoabalancingnetwork ofcouventional design. This balancingnetwork balancesthepotentlalbetweentherotaryarmand ground against astandard potential, i. e.. the standard potential and that betweenground andtherotaryarmareopposedtoproducea differential potential. Thebalancing network is connected to a vibrator li which is coupled to anoscillator l2 and these convert the difference between the standardpotential and that impressed from the rotary arm to ground into analternating current. This alternating current is ampliiled by a highgain A. C. amplifier Il. As described hereinafter, the output oi' theampliner is rectified and the voltage proportional to the amplitude ofthe alternating current is applied to a trip circuit Il, which controlsthe operation of a control relay It which in turn actuates a mass markerlamp Il that marks a mass spectrogram poduced on a photographic i'ilm 41of a recorder I Currents generated through discharge of ion beams at theion collector are amplliled and recorded as a spectrogram on the movingphotographic film l1 by means of a galvanometer il. The mass marker issynchronised with the galvanometer by the mass marker control Justdescribed.

The control relay, in addition to marking the spectrogram. steps up therotary arm Il to the next tap. say T4 of the rotary stepping relay.

'lhe oscillator and vibrator are coupled together because a vibratorcoil il is connected in the output oi the oscillator. A condenser Blconnected in parallel with this coil forms with the coil a parallelresonant network which may be electrically tuned to the same frequencyas the resonant frequency of the mechanical elements of the vibrator.These elements include one normally closed pair l1 of contacts andanother set of contacts comprising an armature contact 0I, a signalcontact Il and a ground contact Il. The amature normally is in theneutral position and contacts the signal contact and the ground contactalternately when alternating current is applied to the vibrator coil.

The high gain A. C. amplifier has a signal grid Il connected to thearmature contact l0 through a shielded conductor 0B. The Signal contactIl is connected through a second shielded conductor 61 to the slider 8lof a potentiometer l! in the balancing network. The positive terminal ofthe potentiometer is connected, as indicated hereinbellore, to therotary arm of the rotary stepping re ay.

'I'he amplier Il includes a resonant circuit tuned to the same frequencyas the oscillator. so as to render the amplifier most sensitive to inputsignal components having this frequency. The output oi' the ampliiler isapplied through the normally closed contacts II of the vibrator to thesignal grid 10 of a relay tube 1i included in the trip circuit Theoutput of the relay tube is applied to a coil 13 which actuates thecontrol relay Il.

A pulse relay 1l is connected in the balancing network Il. It has a pairoi normally open contacts 1| connected between the positive terminal ofthe potentiometer Il and its slider Il.

A conventional regulated power supply Il supplies power to a panel lightli, the marker light A large capacity condenser Il is connected bc- Itween the potentiometer slider and ground. A condenser 02 of smallcapacity is included in the high gain amplifier and ls connected betweenground and the signal grid Il of the first ampliller tube.

The operation oi the mass marker control described hereinbefore is asfollows:

'Ihe beam sweeper reduces the voltage across the potential dividingnetwork in order to shift the separated lon beams across the collectorat the end of the analyzer tube. As the voltage across the Potentialdividing network decreases. the voltage present at any time between therotary arm and ground is balanced against a negative voltage supplied tothe `balancing network from the potentiometer The difference betweenthese two voltages is applied to the large condenser ll.

The amature contact of the vibrator alternately, and at the frequency ofthe oscillator.

comes in contact with the signal contact 6i and the grounded contact 62.so that part of the charge on the large condenser is alternately appliedto the small condenser and then discharged to ground. In consequence, avoltage equal to that appearing across the large condenser isperiodically applied to the control or signal grid oi the amplifier.producing on this grid pulsations having a substantially rectangular,unidirectional wave form. Thus, in effect. the vibrator functions as aninverter. The first amplifier tube has a plate circuit with a resonantLC network and this filters from the amplified signal all componentsother than the fundamental. The latter is thereupon applied to thesecond amplifier tube itil and thence appears at the output of theampliiier.

The normally closed pair of contacts 51 of' the vibrator are open whenthe amplifier output signal voltage is positive and are closed near thenegative peak of the amplifier output voltage. Consequently, negativepulses are applied periodically to a parallel resistance condensernetwork ii which constitutes the grid circuit of the relay tube 1i. Thetime constant of this grid circuit is long compared to the period of thevibrator, so that there is applied to the relay tube a negative biashaving an amplitude corresponding to the excess of the rotary armvoltage over the potentiometer voltage, i. e., corresponding to thedifferential-potential.

When the bias on the relay tube grid lil falls below a threshold valueinherent to the tube. the tube passes current and closes the normallyopen contacts lin of the control relay 45. When this occurs the panellight is illuminated and the marker light 46 marks the spectrograrn, Atthe same time the rotary arm is stepped up to the next tap and thenormally open contacts of the pulse relay are closed momentarily.thereby connecting the positive terminal of the potentiometer Gil to itssliding contact and impressing on the signal grid of the first amplifiertube a large positive potential. This in turn causes a large nega,- tivebias to be applied to the grid oi' the relay tube. thereby opening thecontact of the control relay and the pulse relay. In this condition, theapparatus is ready to make another mark on the mass spectrogram when thetrip circuit again closes the control relay.

By maintaining a proper relationship of resistances between the taps ofthe rotary stepping relay. as described in detail in the aforementionedcopending application of Langmuir. the action of the mass marker issynchronised perfectly with the recording galvanometer. In consequence.as each peak is recorded on the photographic paper a beam of iight marksthe paper adjacent that 'Ihe mass marker described and claimed hereinfires more accurately than one provided with a direct current amplifier.This advantage is achieved through the use of the high gain alternatingcurrent amplier in conjunction with the means for converting the outputof the balance network into alternating curret which is applied to theamplifier. and the means for rectifying the output of the amplifier andapplying the rectified output to the trip circuit. The use of thealternating current amplifier obviates fluctuations in the firingthreshold voltage due to drift. as occurs in certain direct currentamplifiers. Moreover, since the alternating current amplifier has highgain 'any fluctuations in trip-circuit relay tube characteristics becomerelatively unimportant All in all, the apparatus described is anextremely accurate one for correlating specic mass of ions to ionabundance.

The mass marker illustrated includes a plurality of coupledthree-positioned switches III. 12|, ill. Position i on each switch is oposition. Switch III is connected in the power line when on positions 2and l. Switch III is ol! in both positions i and 2, but in position Icompletes the circuit of the lower contacts of the control relay. Inpositions 2 and I the switch |22 connects the battery to the resistanceof the potentiometer I9 The three coupled switches may be thrownsimultaneously from a common control lever, respectively, to positionsi. 2 or l. When the switches are in position i. the circuits, includingthe switches are open. In position l, power is supplied to thepotentiometer B9 and to the regulated power supply. In position I, al1three circuits controlled by the switches are completed.

I claim:

1. In a mass indicator of a mass spectrometer adapted to indicate thespecific masses of ions being detected by the spectrometer and having aresistance, means for impressing across the resistance a voltage whichis a function of the specinc mass being detected and changes inaccordance therewith, and means for selecting successive fractions ofsaid voltage during a period in which the voltage is changing, thecombination which comprises means connected to the voltage selector forproducing an alternating current corresponding in amplitude to theselected fraction of the voltage, and means responsive to a deviation inthe amplitude of the alternating current above a threshold value forindicating the specific mass of ions detected when that threshold isreached and for causing the voltage selector to select the next fractionof voltage.

2. In a mass indicator of a mass spectrometer adapted to indicate thespecic masses of ions being detected by the spectrometer and having aresistance, means for impressing across the resistance a voltage whichis a function of the speclflc mass being detected and changes inaccordance therewith, and means for selecting successive fractions ofsaid voltage during a period in which the voltage is changing, thecombination which comprises means connected to the voltage selector forproducing an alternating current corresponding in amplitude to theselected fraction of thevoltamsaidmeansineludingabalancingnetmanoeciliatorandavihratorcwnledtothr3. In a mass indicator of a mass spectrometer adapted to indicate thespecinc masses of ions acrossthenetworkavoltagewhichisanmction of thespecinc mass being detected and changes voltage selector for producingan alternating cur. rent corresponding in amplitude to the selectedtraction of the voltage. a high gain AC amplier tor amplifying current,and means responsive to a deviation in the amplitude of the alternatingcurrent above a threshold value for indicating the speciiic mass of ionsdetected when that threshold is reached and for causing the voltageselector to select the next traction oi voltage.

4. In a speciiic mass indicator for a mass spectrometer provided with acircuit and means for impressing across the circuit a voltage which is afunction ot the specific mass oi the ions being detected at a giveninstant, the combination which comprises a stepping relay connected insaid circuit and provided with a movable arm making contact withsuccessive points in said circuit and a lead through which the arm isconnested to a terminal. means for opposing the potential between thelead and an end of said circuit against a standard potential, means forconverting the resulting dierential potential into an alternatingcurrent, means for rectifying the a1- ternating current, a mass marker,a control relay which actuates the mass marker and the stepping relay. atrip circuit connected to the control relay, and means for applying tothe trip circuit avoltlgemticnalto the amplitude et therectiedalternatingcurrent. Y

llnamassmarteri'oramassspectrometer having a potential dividing networkthe voltage acroeswhichisatunction o! thespecinc-masofionsbeingdetectedandmeansforselecting progressively diilerentfractions of the voltage acrossthenetworkasthevoltageacrossitdecreases.the combination which comprises means for converting the selectedtraction into altemating current corresponding in amplitude to theselectedtraction.andmeansresponsive toadeviatlon of the amplitude oi'the alternating current from a threshold value tor indicating thespecific mass o! ions which may be detected when that threshold isreached and for selecting s. new frantion ot the voltage across thenetwork.

6. In a mass marker i'or a mass spectrometer having a conductor. meansfor impressing across the conductor a voltage which is a function oi'the speciilc mass oi ions being detected in the spectrometer. and meansfor successively selecting diilerent fractions oi the voltage appliedacross the conductor as that voltage changes, the combination whichcomprises a balancing network adapted to oppose the selected fractionoi' the voltage with a standard potential to produce a diilerentialpotential, an A. C. amplifier, circuit means for applying thediilerential potential to the ampliiier as a series of pulses, a relaytube having a grid and an anode, means for applying rectiiied pulsesfrom the A. C. ampliiier output to the grid of the relay tube,-meansconnected to the anode of the relay tube for altering the selectedfraction of the voltage, said means being operative only when the gridvoltage of the relay tube is greater than a threshold value, and avibrator having one set of contacts for alternately connecting the A. C.amplier to the balancing network and to ground and another pair ofcontacts operating to apply half cycles of the A. C. amblliiler outputvoltages to the grid of the relay tu CLIFFORD E. BERRY.

CERTIFICATE OF CORRECTION.

Patent No. 2,570,651.

March 6, 1914.5.

CLIFFORD E. BERRY.

It is hmy certified that error appears in the printed specification ofthe above'nmbered patent requiring creotion as follows: Page 5, secondcoln, lineylii, for' "curret" read --currentng page il, first column,line 1'?, caiinjl-for "'in" sec occurrence, read -is; and that the SaidLetters Pant should be read with this correction therein that the me mayconform to the .record of the case in the Patent Office.

signes and .enea this 20th day of november, A. D. 19u15.

(Seal) Leslie Frazer First Assistant Camissioner of'. Patents.

voltamsaidmeansineludingabalancingnetmanoeciliatorandavihratorcwnledtothr3. In a mass indicator of a mass spectrometer adapted to indicate thespecinc masses of ions acrossthenetworkavoltagewhichisanmction of thespecinc mass being detected and changes voltage selector for producingan alternating cur. rent corresponding in amplitude to the selectedtraction of the voltage. a high gain AC amplier tor amplifying current,and means responsive to a deviation in the amplitude of the alternatingcurrent above a threshold value for indicating the speciiic mass of ionsdetected when that threshold is reached and for causing the voltageselector to select the next traction oi voltage.

4. In a speciiic mass indicator for a mass spectrometer provided with acircuit and means for impressing across the circuit a voltage which is afunction ot the specific mass oi the ions being detected at a giveninstant, the combination which comprises a stepping relay connected insaid circuit and provided with a movable arm making contact withsuccessive points in said circuit and a lead through which the arm isconnested to a terminal. means for opposing the potential between thelead and an end of said circuit against a standard potential, means forconverting the resulting dierential potential into an alternatingcurrent, means for rectifying the a1- ternating current, a mass marker,a control relay which actuates the mass marker and the stepping relay. atrip circuit connected to the control relay, and means for applying tothe trip circuit avoltlgemticnalto the amplitude et therectiedalternatingcurrent. Y

llnamassmarteri'oramassspectrometer having a potential dividing networkthe voltage acroeswhichisatunction o! thespecinc-masofionsbeingdetectedandmeansforselecting progressively diilerentfractions of the voltage acrossthenetworkasthevoltageacrossitdecreases.the combination which comprises means for converting the selectedtraction into altemating current corresponding in amplitude to theselectedtraction.andmeansresponsive toadeviatlon of the amplitude oi'the alternating current from a threshold value tor indicating thespecific mass o! ions which may be detected when that threshold isreached and for selecting s. new frantion ot the voltage across thenetwork.

6. In a mass marker i'or a mass spectrometer having a conductor. meansfor impressing across the conductor a voltage which is a function oi'the speciilc mass oi ions being detected in the spectrometer. and meansfor successively selecting diilerent fractions oi the voltage appliedacross the conductor as that voltage changes, the combination whichcomprises a balancing network adapted to oppose the selected fractionoi' the voltage with a standard potential to produce a diilerentialpotential, an A. C. amplifier, circuit means for applying thediilerential potential to the ampliiier as a series of pulses, a relaytube having a grid and an anode, means for applying rectiiied pulsesfrom the A. C. ampliiier output to the grid of the relay tube,-meansconnected to the anode of the relay tube for altering the selectedfraction of the voltage, said means being operative only when the gridvoltage of the relay tube is greater than a threshold value, and avibrator having one set of contacts for alternately connecting the A. C.amplier to the balancing network and to ground and another pair ofcontacts operating to apply half cycles of the A. C. amblliiler outputvoltages to the grid of the relay tu CLIFFORD E. BERRY.

CERTIFICATE OF CORRECTION.

Patent No. 2,570,651.

March 6, 1914.5.

CLIFFORD E. BERRY.

It is hmy certified that error appears in the printed specification ofthe above'nmbered patent requiring creotion as follows: Page 5, secondcoln, lineylii, for' "curret" read --currentng page il, first column,line 1'?, caiinjl-for "'in" sec occurrence, read -is; and that the SaidLetters Pant should be read with this correction therein that the me mayconform to the .record of the case in the Patent Office.

signes and .enea this 20th day of november, A. D. 19u15.

(Seal) Leslie Frazer First Assistant Camissioner of'. Patents.

